Abstract: An azimuthal scanning antenna for an aircraft landing system is formed of a set of vertically disposed columnar radiators arranged side-by-side in a horizontal array. The columnar radiators are tilted back in pitch 7.5.degree.. Individual ones of the radiators are formed of waveguide sections terminated by reflecting end walls. The terminating walls provide for a standing wave of electromagnetic field in response to microwave electromagnetic energy applied to the waveguide section by a feed disposed at or near the bottom of the waveguide section. Slot apertures are disposed along a front wall of each waveguide section, and are oriented at a selected angle relative to a perpendicular relationship to the sidewalls. The orientation of the slots introduces a variation in coupling for illumination of the radiation aperture of the radiator wherein the phase center is offset from a central point towards an upper end of each of the waveguide sections.

Abstract: The present invention achieves the above objects, among others, by providing apparatus for converting a supplied AC input signal into an AC output signal having a selected lower frequency than the frequency of the AC input signal, which apparatus translates individual half cycles of the supplied AC input signal to an intermediate output signal with selected amplitude and polarity such that during successive pairs of first and second periods, each such period corresponding to a predetermined number of half cycles of the AC input signal, the translated half cycles of the AC input signal all have the same first selected polarity during each first period and have the same second selected polarity during each second period, with the first and second polarities being opposite. The apparatus filters the intermediate output signal to develop the AC output signal having the selected lower frequency.

Abstract: Multi-system or "universal" AM stereo receivers are provided which require no switching of the receiver's stereo decoder circuitry regardless of which AM stereo system signal is being received. In accordance with one aspect of the invention, acceptable stereo sound is achieved for all AM stereo systems by introducing a selected amount of distortion correction in the L-R channel of the universal receiver and a selected phase difference between the L+R and L-R channels. In addition, perceived stereo separation in AM stereo and other stereo receivers is enhanced by also properly selecting the gain in the L-R channel in relation to the L+R channel.

Abstract: A noise trap circuit particularly suitable for use in an electro-acoustic system, operates to suppress low level signals or noise while allowing a relatively large signal to pass unattenuated between input and output terminals of the circuit. Blocking elements between the input and output terminals establish a high impedance path to the noise but switch to a conductive state when the large signals are present at the input terminals. Shunt elements across the output terminals provide a low resistance path or "crowbar" when only the noise is present at the input terminals, but switch to a non-conductive state when the large signals are sensed at the circuit input.

Abstract: A surface wave acoustic delay line is formed of a set of electrode assemblies disposed on the surface of a block of crystalline material propagative of a surface acoustic wave. In each of the assemblies, the electrodes are arranged in an interdigitated pattern. Reflected waves are cancelled by the construction of an additional electrode in each of an electrode assembly, the additional electrode extending only one-half the distance of the other electrodes and being spaced from an adjacent electrode by one-quarter wavelength. This introduces a 180.degree. phase shift between portions of relected waves which then cancel to remove the reflection. Also, in the case of closely spaced electrode assemblies, additional electrodes, equal in shape and size to the electrodes of the assemblies, are introduced between the assemblies in the form of a grid which propagates surface waves without reflection.

Abstract: An apparatus for supporting a large volumetric array of acoustic sensors in water is packaged in a standard configuration sonobuoy envelope and utilizes conventional sonobuoy deployment components. A housing within the envelope contains a plurality of tubular extendable members stored on drums and extendable to form array support booms upon deployment of the apparatus. A plurality of releasable array modules are releasably attached to the housing, each module containing an array cable and a plurality of acoustic sensors secured to and along the cable. As the apparatus enters and descends through the water, the tubular members extend to form array support booms. The array modules are synchronously released to the extension of the tubular members and as the modules descend, the array cables and acoustic sensors deploy, the array cables forming catenaries between points on array support boom pairs or between the housing and points on the various booms.

Abstract: An MLS system having redundant subsystems. Dual signal sources feed dual power dividers. A first switch array selects the power divider to be used and provides the selected signals to an array of phase shifters. A second switch array provides the phase shifted signal, which may be amplified, to either a primary array having elements for radiating a scanning beam or a recombining network having outputs connected to auxiliary antennas. A third switch array provides control signals to the array of phase shifters from either a main beam steering unit or a standby beam steering unit. Alternatively, the dual signal sources feed a single power divider through a circulator. Duplicate auxiliary antennas may be used with antenna switches located before the power dividers or circulator for selectively providing the signals to the auxiliary antennas instead of the primary array.

Abstract: The fault monitoring function of an executive monitor contained in a microwave landing system is verified by evaluating a history of the parametric information sampled by an executive monitor and storing in memory the number of out of tolerance parametric signals received from an antenna means over a predetermined time period, replacing the stored number of out-of-tolerance parametric signals with a predetermined number that will be beyond a second predetermined limit if another out-of-tolerance parametric signal is added to said number, adding one such internally generated out-of-tolerance parametric signal to said predetermined number, generating an alarm if said sum is beyond the second predetermined limit, and restoring the previously stored number of out-of-tolerance parametric signals received from the antenna means if the alarm was generated, and shutting the system down if an alarm was not generated.

Abstract: A method and apparatus for performing integration using a circuit capable of integrating an input signal over a wide linear dynamic range. The circuit modulates the input signal with a biphase signal having positive and negative phases. The modulated signal is then provided to an integrator. The integrator operates continuously within its linear range without needing charge dumping because the amplitude of the modulated signal is less than the amplitude required to saturate the integrator. Each interval of the integrated signal corresponding to positive and negative phases of the biphase signal is then partitioned into intervals corresponding to the positive phase and intervals corresponding to the negative phases by two track and hold circuits with alternating tracking and holding periods. The signal intervals corresponding to the negative phase of the biphase signal are subtracted from the intervals corresponding to the positive phases by a differential amplifier.

Abstract: Successive MLS scanning signals are received as pulse-type analog signals and converted into corresponding digital signals. The centroid of each digital signal is determined at at least two different levels below the peak of the digital signal. The centroids for each signal are averaged, whereby the average represents the centroid of the corresponding received pulse-type signal.

Abstract: A central aperture provides at least two radiation pattern modes. A second aperture concentric with the central aperture provides at least two radiation pattern modes. A first feed system excites the central aperture and a second feed system excites the concentric aperture. Circuit means associated with the second feed system provides an auxiliary excitation to the concentric aperture which results in optimizing the radiation pattern obtained during excitation of the central aperture.

Abstract: A beamforming adaptive control loop is simultaneously employed in combination with a null-steering adaptive control loop to enhance the signal/interference ratio resulting in an increase in the messasge quality. The loops may employ temporal processing in which case on-epoch sample/hold filters and off-epoch sample/hold filters form separate loops which enhance the desired signal and cancel the undesired signal, respectively. The correlated output from the beamforming loop is added to the correlated output of the null-steering loop and mixed with the incoming signal.

Abstract: In order to recover the original audio modulation samples when using a continuous code change, sampled data, spread spectrum waveform structure, a dedicated message matched filter is used to process data from multiple emitters within the same range interval. The dedicated message matched filter is matched to an incoming signal only at the precise time of the message epoch. The matched filter coding corresponding to the arrival time of message epochs as derived from synchronization acquisition circuitry is rapidly switched so that one dedicated message matched filter can be used to process data from multiple users simultaneously.

Abstract: A system for synchronizing a succession of horizontal deflection coil currents of a CRT display with a succession of synchronization signals includes a variable delay which is strobed by a synchronization signal and triggers the generation of a deflection current after a specified delay. The delay is automatically controlled by a feedback loop in which the present delay is measured by a set-reset flip-flop, the flip-flop providing an output pulse having a duration equal to the delay. An integrator averages a train of output pulses from the flip-flop, and combines a reference signal with the average value to provide the control signal for the delay. The system operates with minimal bandwidth and with dynamics which are free of acquisition constraints so as to provide minimal sensitity to noise.

Abstract: Proper operation of a system fault monitor is verified while the monitor is coupled on-line with the system and to an alarm line. During periods when actual system signals are produced, the monitor is coupled through one of two time delay circuits to the alarm line. During periods when no actual signals are produced by the system, the monitor input is switched to an error signal generator and the monitor output is coupled through the other time delay circuit to processing circuitry which detects the presence of the alarm signal after the circuit time delay. If no alarm signal is detected, a failure of the monitor and/or delay circuit is indicated.

Abstract: A remote monitoring system (RMS) receiver which operates at a dual baud rate. The operating rate is selected to be the same as the rate being used by remote equipment originating the data link with the receiver. A modem associated with the receiver provides an indicator signal indicating phase shift keying (a high baud rate) or frequency shift keying (a low baud rate) is being received from the remote equipment. The indicator signal is used to select the baud rate of a programmable baud rate generator of the RMS receiver. This controls the baud rate signal which is supplied to an asynchronous interface controlling data transfer between the receiver and the modem.

Abstract: Proper operation of a beam steering unit for a phase array antenna, is verified by simulating the pattern of wave energy which would be radiated to an observation point in space when the beam steering unit is connected to phase shifters associated with elements of the antenna. The simulated pattern thus obtained may be compared with a preset pattern for the observation point during a scanning operation of the beam steering unit, and an alarm or other indication is obtained when the difference between the simulated and the preset pattern exceeds a certain limit. The simulated pattern is obtained by storing phase angle data from the beam steering unit in a memory at areas corresponding to phase shifters associated with elements of the phased array antenna.Observation angle data corresponding to the angle of the point in space relative to the antenna array is generated, the observation angle data being a function of observation angle, antenna element spacing and radiation wavelength.

Abstract: A color monitor having a highly accurate video processing circuit for providing a high accuracy color CRT display is disclosed which utilizes three feedback loops in each of the three primary color channels, each feedback loop including both the final video amplifier and the CRT in order to achieve equalization and stabilization of their combined signal-to-brightness transfer characteristics against both CRT and circuit drift. The video processor circuitry also includes a D/A converter for generating a signal representative of the desired amplitude component for each primary color from a three bit digital input. By utilizing the three feedback loops, the color produced in the CRT display is independent of the operator set brightness and contrast settings and is maintained to within 10% of its desired value over varying temperature and adverse environmental conditions.

Abstract: A transistor circuit is provided with a symmetrical floating configuration for attaining multifunction operation of a transistor having symmetrical source and drain characteristics, preferably a GaAs MESFET. The circuit includes a balun which may be configured as a transformer, a differential amplifier, or a magic-tee waveguide depending on the frequency of signals to be processed by the circuit. Balanced terminals of the balun may be directly or capacitively coupled to source and drain terminals of the transistor. Tuning circuits are employed for applying signals having different frequencies to the transistor and for extracting intermodulation products generated by the transistor in response to the signals at the different frequencies. With the direct connection between the balun and the transistor, alternating voltages may be impressed between the terminals of the transistor to alternate source and drain regions of the transistor.

Abstract: The amplitude of a signal to be modulated on a carrier wave is sampled every T seconds. The sampled amplitudes are converted into phase representative pulses of pulse rate 1/T. Each phase representative pulse corresponds to the difference between a first phase corresponding to the sampled amplitude and the phase of Nth previous phase representative pulse, where N is an interger greater than 1. The discrete phase representative pulses are phase modulated onto the carrier wave. Conversion is accomplished by detecting the sampled amplitudes, applying the detected amplitudes as an address to a ROM to provide corresponding differential phase information, and modulating the differential phase information onto the carrier. To demodulate the signal from the carrier wave, the carrier wave is delayed for NT seconds and the delayed signals are subtracted from the undelayed signals.